The hallmark of systemic sclerosis (SSc) is excessive connective tissue accumulation and increased numbers of fibroblasts/myofibroblasts that produce matrix but are refractory to upregulation of matrix metalloproteinase-1 (MMP-1) in the dermis and organs (e.g. lungs) involved in the disease. It has been assumed that the increased numbers of fibroblasts/myofibroblasts present in the fibrogenic lesions of SSc arise from proliferation and growth of local fibroblasts. In addition to this local source for fibroblasts/myofibroblasts in SSc lesions, we present evidence in this proposal that the blood may also be an important source for such cells. We have observed that SSc peripheral blood mononuclear cells (PBMC) when cultured for 5 days with native type l collagen (CI) or constituent alpha chains and then for >21 days gives rise to fibroblast-like cells (FLC) which stain positive for fibroblast and myofibroblast markers, synthesize CI, CIII and hyaluronic acid but do not upregulate MMP-1 in response to inflammatory cytokine stimulation. We believe this observation has major implications for a new understanding of SSc pathogenesis. This project proposes a detailed analysis of the FLC outgrowth phenomenon. It will test the hypothesis in the 1st 2 specific aims that FLC outgrowth from SSc PBMC cultured with CI in vitro is correlated with the degree of cell-mediated immunity to CI and that downregulation of the immune response by oral tolerance induction to CI will be associated with decreased outgrowth of FLC from PBMC cultured with CI. Additional studies will determine whether the degree of immunity to CI in SSc patients and/or modified Rodnan skin score and/or disease duration correlate with degree of outgrowth of FLC from Cl-stimulated PBMC cultures; determine which cytokines/growth factors are associated with FLC outgrowth and whether such identified cytokines/growth factors can trans differentiate PBMC precursors into FLC; identify which alpha1 (l) and alpha(l) l cyanogen bromide peptides induce FLC outgrowth from SSc PBMC; and what is the spectrum of the types of FLC grown from Cl-stimulated SSc PBMC. These studies should provide clues not only to pathogenetic mechanisms of fibroblast accumulation in SSc lesions, but should also provide clues to new therapeutic approaches for treating this disease.